Synergistic in situ thermal management and deposition control for enhanced weldability of metastable high manganese austenitic steels in flux-cored arc welding

Abstract

High-manganese austenitic steels (e.g., Mn13) are critical for railway applications due to their exceptional work-hardening capacity, but their welding remains challenging due to carbide embrittlement and grain coarsening in the heat-affected zone (HAZ). This study proposes an integrated welding strategy combining in situ substrate cooling and multi-layer deposition during flux-cored arc welding (FCAW) to control thermal cycles, microstructure, and mechanical properties. The effects of four substrate cooling conditions—air (25 °C), water (20 °C), ice (0 °C), and ice + salt (−20 °C)—and one to three weld layers were systematically investigated. Results show that ice + salt cooling at −20 °C combined with three-layer deposition reduced the HAZ width by 56% (from 8.0 to 3.5 mm) and minimized the hardness gradient between weld metal and HAZ from Δ40.07 to Δ15.09 HV. Rapid cooling at 0.46 °C/s suppressed carbide precipitation, refined austenite grain structure, and shortened exposure in the critical embrittlement temperature range (400–900 °C). Microstructural analysis confirmed transition from coarse dendritic grains under air cooling to fine equiaxed grains with limited carbide networks under active cooling. The proposed approach effectively balances fusion integrity with microstructural homogeneity, offering a practical and scalable method to enhance the durability and performance of welded high-Mn steel components in demanding service environments.